Anti-shock control devices for electrically heated glass



Sept. 1 1970 D. J. AISANICH ETAL 3,526,753

ANTI-SHOCK CONTROL DEVICES FOR ELECTRICALLY HEATED GLASS 2 Sheets-Sheet1 Filed Dec. 8. 1966 -F1G.Z

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Sept. 1, 1970 J A|$AN|H ETAL 3,526,753

ANTI-SHOCK CONTROL DEVICES FOR ELECTRICALLY HEATED-GLASS Filed Dec. 8,1966 2 Sheets-Sheet 2 United States Patent 3,526,753 ANTI-SHOCK CONTROLDEVICES FOR ELECTRICALLY HEATED GLASS Daniel J. Aisanich and Frederic A.Richter, Chicago, Ill.,

assignors to Ardco, Inc., Chicago, 11]., a corporation of Illinois FiledDec. 8, 1966, Ser. No. 600,201 Int. Cl. H05b 1/02 US. Cl. 219-522 21Claims ABSTRACT OF THE DISCLOSURE A current responsive control relaydevice effectively disconnects the power from electrically heated glasswhen breakage occurs, to obviate any shock hazard. In the firstembodiment, the relay device comprises a bimetal switch which isoperated from a first to a third position by a voltage responsiveheater. The bimetal switch is maintained in the third position by theheat generated in the bimetal by the flow of the main load current. Whenbreakage of the heater occurs, the bimetal switch returns to anintermediate position, in which it is maintained by a reduced currentthrough the voltage responsive heater. In the second embodiment, therelay device comprises a normally open bimetal switch across which ahigh value resistor is connected. The bimetal switch is closed by theheat developed in such resistor, and is kept closed by the heatgenerated in the bimetal itself by the main load curent, and also theheat generated in a series con nected resistor. When breakage of theelectrically heated glass occurs, the bimetal switch is opened. Theresistor has a high value to obviate any shock hazard. Inthe fourthembodiment, the series connected resistor is not needed. In the fifthembodiment, a compensating bimetal is employed to carry one of thecontacts for the bimetal switch, to compensate for variations in theambient temperature. In the third embodiment, the relay device comprisesnormally open contacts operable by an electromagnet having a voltageresponsive coil and a current responsive coil. The voltage responsivecoil is connected across the contacts so as to cause initial closurethereof. Such closure is maintained by the load current through thecurrent responsive coil. The voltage responsive coil has a highresistance to obviate any shock hazard.

This invention relates to electrically heated glass panels and pertainsparticularly to control devices for obviating any electrical shockhazard when such glass panels are accidentally broken.

An electrically heated glass panel generally comprises a plurality ofparallel panes of glass. An electrically conductive coating, layer orthe like is provided on one of the inaccessible or inner surfaces of oneof the panes. The glass panel is heated by causing an electrical currentto pass through the electrically conductive coating. Electrically heatedglass has many applications, but is particularly useful for refrigeratordoors. Display doors utilizing electrically heated glass are frequentlyemployed on refrigerated cabinets and compartments for supermarkets andother stores, to hold frozen foods, ice cream, dairy products and otherfoods and beverages requiring refrigeration. The electrical heating ofthe glass prevents the condensation of moisture on the glass. Suchcondensation tends to occur under conditions of high atmospherichumidity, even though the glass is of the insulating type, having aplurality of parallel panes with dead air spaces therebetween.

Under normal conditions, electrically heated glass does not present anyshock hazard, because the electrically conductive coating or element isbetween the panes of glass and is inaccessible. However, if breakage ofthe 3,526,753 Patented Sept. 1, 1970 "Ice glass occurs due to someaccident, the electrically conductive coating or other element maybecome accessible to the touch so that an electrical shock hazard maypossibly exist.

The general object of the present invention is to obviate any such shockhazard when electrically heated glass is accidentally broken.

A further object is to provide a new and improved control device wherebythe electrical power is effectively disconnected from the electricallyheated glass when breakage occurs. The supply of power may bedisconnected entirely, or may be so diminished that no shock hazard willexist.

Another object is to provide a new and improved control device or relaywhich effectively disconnects the electrical power in response to theinterruption of the heating current due to the breakage of the glass.

A further object is to provide a new and improved control device whichis effective to supply substantially full power to the electricallyheated glass under normal conditions, while being operative to terminateor diminish the supply of power to a harmless level, when the heatingcurrent is interrupted by the breakage of the glass.

Another object is to provide a new and improved control device whichutilizes a relay arrangement for applying full power initially and formaintaining the full supply of power as long as the heating current isuninterrupted, while being effective to disconnect or diminish the powerwhen the heating current is interrupted by the breakage of the glass.

A further object is to provide a control device of the foregoingcharacter in Which the relay arrangement may be of the thermal ormagnetic type.

Another object is to provide such a new and improved control devicewhich is effective and dependable in operation, yet is low in cost.

Further objects and advantages of the present invention will appear fromthe following description taken with the accompanying drawing, in which:

FIG. 1 is a diagrammatic illustration of an anti-shock control device tobe described as one embodiment of the present invention.

FIG. 2 is a circuit diagram of a modified anti-shock device constitutinga second embodiment.

FIG. 3 is a diagrammatic illustration of a third antishock device,constituting another embodiment.

FIG. 4 is a circuit diagram of a modified anti-shock device,constituting a fourth embodiment, similar to that illustrated in FIG. 2.

FIG. 5 is a diagrammatic illustration of another antishock device,constituting a fifth embodiment, which is compensated for ambienttemperature variations.

FIG. 6 is a circuit diagram of another modified antishock device,similar to the one illustrated in FIG. 1.

FIG. 7 is an elevational view showing the mechanical construction of theanti-shock device represented by FIG. 4.

FIG. 8 is an end view of the device shown in FIG. 7.

FIG. 9 is an elevational view of the anti-shock device represented byFIG. 5.

As already indicated, FIG. 1 illustrates an anti-shock control device 10which is employed to control the supply of electric power to anelectrically heated glass panel 12. Such glass panels are applicable torefrigerators of all kinds, both domestic and commercial, but areparticularly valuable for display-type refrigerators as employed insupermarkets or other stores. Thus, the illustrated panel 12 is shown inan application in which it is mounted in a display refrigerator door 14,which may be of the general type disclosed and claimed in the KurowskiPat. Nos. 2,987,782 and 3,131,421.

The illustrated glass panel 12 comprises three parallel panes 16, 17 and18 with spacers 19 and 20 between the edge portions thereof. However,the panel may comprise more or less than three panes. Thus, the panelmay have two, four or even more panes of glass.

The illustrated panes 16, 17 and 18 are mounted in a frame or retainer22. Insulating spaces 24 and 25 are provided between the panes 16-18.The spaces 24 and 25 are normally filled with dry air, which providesgood heat insulation and obviates any condensation of moisture in thespaces 24 and 25. The door 14 comprises an outer frame 26, preferablymade of metal, in which the glass panel 12 is mounted.

An electrically conductive coating or layer 28 is provided on one of theinaccessible surfaces of one of the panes 16-18. Such coatings are knownto those skilled in the art. The coating 28 may be transparent so thatit does not interfere with visibility through the glass panel. Thecoating 28 may be intimately bonded or fused to the glass pane. In theillustrated construction, the conductive coating 28 is on the rearsurface of the front or outer pane 17.

Suitable leads 30 and 32 are connected to the conductive coating 28adjacent the opposite edges of the glass panel 12. The leads 30 and 32are brought out of the edges of the glass panel so that electrical powermay be supplied thereto.

The electrical power is derived from an ordinary electrical line 34comprising line wires 36 and 38. The electrical line 34 may be adaptedto supply alternating current at 110 volts and 60 cycles, or any othersuitable voltage and frequency.

The control device 10 is connected between the line 34 and theelectrically heated glass panel 12 and is effective to supply fullelectrical power to the glass panel during normal operation. If theglass panel is broken, the control device 10 disconnects the electricalpower from the glass panel so that no shock hazard will exist, eventhough the broken edges of the conductive coating 28 are accessible tothe touch.

The illustrated control device 10 comprises a thermal relay or switchingdevice 40 utilizing a bimetallic strip or bimetal 42. A contactor orswitch member 44 is mounted on the free end of the bimetal 42. When thebimetal 42 is at room temperature, the contactor 44 engages a switchcontact 46. If the bimetal 42 is heated, it curls so as to cause thecontactor 44 to move from the first contact 46 to a second contact 47,and then to a third contact 48.

The bimetal 42 is provided with a heating element or resistor 50 whichis voltage responsive and is connected between the first contact 46 andthe line wire 38. The other line wire 36 is connected to the stationaryor mounted end of the bimetal 42. A resistor 52 is connected between thesecond contact 47 and the line wire 38. The third contact 48 isconnected to the lead 30 which extends to the conductive coating 28. Theother lead 32 is connected to the line wire 38.

Initially, the contactor 44 on the bimetal 42 engages the contact 46.When power is supplied to the line 34, current flows from the line wire36 through the bimetal 42 and the contactor 44 to the contact 46, andthen through the resistor 50 to the line wire 38. Considerable heat isthus generated in the resistor 50. It will be understood that theresistor 50 is closely adjacent the bimetal 42, so that the heat isquickly transmitted from the resistor to the bimetal. As a result, thebimetal 42 is caused to curl, so that the contactor 44 engages thecontact 47, and then the contact 48. The circuit through the resistor 50is broken as soon as the contactor 44 moves away from the contact 46,but the contactor 44 does not return to the contact 46, but ratherovershoots past the contact 47 to the contact 48. This overshootingaction is due to the rapid heating of the resistor 50, in conjunc- 4tion with the somewhat delayed transmission of heat to the bimetal 42.

When the contactor 44 engages the contact 48, the main power circuit isestablished through the bimetal 42 and the conductive coating 28 on theelectrically heated glass 12. The resulting current through the bimetal42 is quite great, so that the bimetal is heated to a considerableextent by direct resistance heating. The bimetal 42 is heated to such anextent that it maintains its curl so that the contactor 44 continues toengage the contact 48.

This condition prevails as long as the glass panel 12 is unbroken sothat it draws its normal current from the power line 34. If the glasspanel is broken due to some accident, the heating current through thebimetal 42 is interrupted. As a result, the bimetal 42 loses some of itscurl so that the contactor 44 returns to the contact 47. In thisposition, a circuit is established through the bimetal 42 and theresistor 52, between the line wires 36 and 38. The resulting currentthrough the resistor 52 is less than the normal load, but is sufiicientto maintain the temperature of the bimetal so that the contactor 44continues to engage the contact 47. Thus, the electrical power issupplied to the resistor 52, rather than to the glass panel 12, so thatthe power is completely disconnected from the glass panel 12. It will benoted that the line wire 38 is grounded, while the line wire 36 isungrounded. Thus, the disconnection of the glass panel 12 from the linewire 36 is suflicient to obviate any electric shock hazard.

If the electric power is disconnected from the line 34, the controldevice 10 is de-energized, so that the bimetal 42 returns to its initialposition, in which the contactor 44 engages the contact 46. The glasspanel 12 may then be replaced with a new unit, so that the system willbe ready to go into normal operation.

FIG. 2 illustrates a modified control device which is adapted todiminish the supply of electric power to a harmless level, if the glasspanel 12 is broken. In FIG. 2 and the subsequent figures, the conductivecoating or heating element 28, constituting the normal resistive load,is shown symbolically. In the control device 60 of FIG. 2, the heatingelement 28 is adapted to be connected across the line wires 36 and 38through a resistor 62, a bimetal 64, and a pair of contacts 66 and 68.The resistors 62 is of a small value and is connected between the linewire 36 and the stationary or mounted end of the bimetal 64. The contact66 is carried on the free or movable end of the bimetal 64. The contact68 is adapted to be engaged by the contact 66 and is connected to theungrounded lead 30 running to the heating element 28. The bimetal 64 isadapted to be heated by a resistor which is connected between thecontact 68 and the stationary end of the bimetal 64. The resistor 62 isalso adapted to heat the bimetal 64. It will be noted that the resistor62 is effectively in series with the contacts 66 and 68, while theresistor 70 is effectively connected across the contacts.

Before power is applied to the line 34, the bimetal 64 is in theposition shown in FIG. 2, so that the contact 66 is out of engagementwith the contact 68. When power is applied to the line 34, current flowsthrough the series circuit comprising the resistors 62 and 70 and theheating element 28. The resistor 70 is of a relatively high value, sothat considerable heat is generated therein by the application of theline voltage. As a result, the bimetal 64 is heated so that it curls insuch a direction that the contact 66 engages the contact 68. The normalheating circuit is thus completed through the resistor 62, the bimetal64, the contacts 66 and 68, and the heating element 28. The resistor 70is bypassed or short-circuited by the bimetal 64 and the contacts 66 and68, so that the resistor 70 is no longer heated to any substantialextent. However, the resistor 62 is heated sufficiently by the normalload current through the heating element 28, with the result that thebimetal 64 is maintained in a curled position, so that the contacts 66and 68 are held closed.

If the glass heating element 28 is broken due to some accident, the loadcurrent is interrupted so that the resistor 62 is no longer heated.Thus, the contact 66 is moved out of engagement with the contact 68. Asa result, the resistor 70 is switched into the circuit between theungrounded power line 36 and the ungrounded lead 30 to the heatingelement 28. The resistor 70 is of a sufficiently high value to obviateany shock hazard at the ungrounded side of the heating element 28. Thus,the resistor 70 so diminishes the supply of power to the broken heatingelement 28 that the power may be considered to have been etfectivelydisconnected. If anyone should happen to touch the broken heatingelement 28, he will not receive a hazardous shock.

The control devices described thus far utilize thermal control relays,but other types of relays or switching devices may be employed,including magnetic relays and electronic switching devices. Thus, FIG. 3illustrates a modified control device 80 utilizing a magnetic relay 82.It will be seen that the relay 82 comprises two coils 84 and 86, both ofwhich are adapted to operate a movable armature 88, so as to close apair of switching contacts 90 and 92. In the illustrated control devices80, the coil 84 has a large number of turns and a high electricalresistance and impedance, while the coil 86 has a relatively smallnumber of turns and a low electrical resistance and impedance. The coil84 is voltage responsive and connected between the ungrounded line wire36 and the ungrounded lead 30 running to the heating element 28. Thecoil 86 is current responsive and is connected in a series circuit withthe contacts 90 and 92 between the ungrounded line wire 36 and theungrounded lead 30.

When voltage is supplied to the line 34, voltage develops across theopen contacts 90 and 92 so that current flows through the series circuitcomprising the coil 84 and the heating element 28. As a result, thearmature 88 is actuated so as to close the contacts 90 and 92. Thenormal load current then flows through the series circuit comprising thecoil 86, the contacts 90 and 92, and the heating element 28. The highresistance coil 84 is effectively bypassed by the series circuitcomprising the low resistance coil 86 and the contacts 90 and 92. Theenergization of the coil 86 holds the contacts 90 and 92 closed.

If the heating element 28 is broken due to some accident, the normalload current is interrupted. Thus, the coil 86 is de-energized so thatthe relay 82 drops out. As a result, the contacts 90 and 92 are opened.The coil 84 is of such a high resistance that only an insignificant andharmless amount of power is supplied to the ungrounded lead 30.Accordingly, the shock hazard is obviated and the broken heating element28 is effectively disconnected from the power line 34.

- FIG. 4 illustrates another modified control device 100 which issimilar to that illustrated in FIG. 2, except that the separate seriesresistor 62 is not needed, because the bimetal 64 is heated sufficientlyby direct resistance heating. Thus, the line wire 36 is connecteddirectly to the stationary or mounted end of the bimetal 64.

In the control device 100, the contacts 66 and 68 are initially open.When power' is applied to the line 34, a small current flows through theresistor 70 and the heating element 28. The resistor 70 is rapidlyheated so that the adjacent bimetal 64 is caused to curl. As a result,the contact 66 engages the contact 68. This closes the normal heatingcircuit, so that the normal load current flows through the bimetal 64and the contacts 66 and 68 to the heating element 28. The load currentcauses heating of the bimetal 64 due to its own resistance. This heatingis suflicient to maintain the bimetal 64 in a curled position, so thatthe contacts 66 and 68 remain closed.

If the heating element 28 is broken, the normal load current no longerflows through the bimetal 64 so that it cools off and causes thecontacts 66 and 68 to open. The high value resistor 70 is thusintroduced into the circuit between the ungrounded line wire 36 and theungrounded lead 30. The resistor 70 is of such a high value that noshock hazard exists at the ungrounded lead 30.

FIG. 5 illustrates another modified anti-shock control device which issimilar to that illustrated in FIG. 4, except that the device of FIG. 5is compensated for variations in the ambient or atmospheric temperature.The device 110 of FIG. 5 is adapted to operate in a consistent mannerover a wide range of ambient temperature varia tions.

It will be seen that the control device 110 of FIG. 5 employs thebimetal 64, the contacts 66 and 68 and the resistor 70, as previouslydescribed. However, the contact 68 is mounted on a compensating bimetal112, rather than on a stationary support. The compensating bimetal 112is adapted to curl with changes in the ambient temperature, so as tomaintain the relationship between the contacts 66 and 68 unchanged,despite the ambient temperature variations. Thus, the compensatingbimetal 112 moves the contact 68 with changes in the ambienttemperature, to follow the similar movements of the contact 66, due tothe effects of ambient temperature variations upon the bimetal 64.

It will be seen that the compensating bimetal 112 is remote from theheating resistor 70, which is adjacent the main bimetal 64. Moreover,the load current does not pass through the bimetal 112. Thus, aside fromthe compensating action of the bimetal 112, the operation of the controldevice 110 of FIG. 5 is the same as described in connection with FIG. 4.Initially, the resistor 70 heats the bimetal 64 so that the contacts 66and 68 are closed. Thereafter, the load current heats the bimetal 64 bydirect resistance heating. If the heating element 28 is broken, theinterruption of the load current causes the bimetal 64 to cool so thatthe contacts 66 and 68 are opened.

FIG. 6 illustrates another modified anti-shock device which is the sameas that illustrated in FIG. 1, except that the resistor 52 is replacedwith a resistor 122 which is connected between the contacts 46 and 47.The resistor 122 may be of a higher value than the resistor 52.

The operation of the control device 120 is the same as described inconnection with FIG. 1, except for the manner in which the contactor 44is maintained in engagement with the contact 47 when the glass heatingelement 28 is broken. The breakage of the heating element 28 interruptsthe load current, with the result that the bimetal 42 cools oif andstarts to move back toward its initial position. When the contactor 44engages the contact point 47, a circuit is established between the linewires 36 and 38, through the bimetal 42, the contactor 44, the contact47, the resistor 122 and the resistor 50. The current in this circuitheats the bimetal 42 to such an extent that the contactor 44 ismaintained in engagement with the contact 47. Because of the high valueof the resistor 50, only a small current is needed in this circuit.Thus, the resistor 122 may also be of a high value. If desired, theresistor 122 may be located near the bimetal 42 so that the bimetal isalso heated by the heat generated in the resistor 122. The heatgenerated in the resistors 50 and 112 is insufficient to cause thecontactor 44 to move against the contact 48. Thus, the broken heatingelement 128 remains disconnected from the un grounded power line 36.

By way of example, FIGS. 7 and 8 illustrate a mechanical constructionwhich may be employed for the antishock control device 100 as shown inFIG. 4. It will be seen that the bimetal 64 is in the form of a helicalribbon 124 which is coiled around the resistor 70. As shown, theresistor 70 comprises a generally cylindrical body 126 having end leads128 and 130 extending axially from the opposite ends thereof. One end ofthe helical ribbon 124 is soldered, welded or otherwise secured to thelead 128 to form a joint 132. The movable contact 66 is soldered, weldedor otherwise secured to the free end of the helical coil 124. It will beseen that the fixed contact 68 is mounted on a strip or other support134, which is soldered, welded or otherwise secured to the lead 130, toform a joint 136.

When the resistor 70 heats the helical bimetallic strip 124, it curls ina counter-clockwise direction, as seen in FIG. 8, so that the contact 66moves against the contact 68. During normal operation, the load currentpasses along the helical bimetallic strip 124 and heats it to such anextent that the contacts 66 and 68 are kept closed.

FIG. 9 illustrates a mechanical construction for the compensated controldevice as shown in FIG. 5. It will be seen that the compensating bimetal112 takes the form of a helical bimetallic strip 142 which is coiledaround the end lead 130 of the resistor 70. One end of the helical strip142 is soldered, welded or otherwise secured to the lead 130 to form ajoint 144. The contact 68 is mounted on the free end of the bimetallicstrip 142, adjacent the contact 66. To prevent the bimetallic strip 142from carrying the full load current, a flexible pig-tail lead 146 isconnected between the contact 68 and the end lead 130.

In the construction of FIG. 9, the bimetallic strip 142 is arranged tocurl in such a direction as to compensate for the curling of the mainbimetallic strip 124 due to ambient temperature variations. Withincreasing ambient temperature, the main bimetallic strip 124 becomescurled more tightly, while the compensating bimetallic strip 142 becomescurled less tightly. Thus, the relationship between the contacts 66 and68 is kept substantially the same. The main bimetallic strip 124 iswound with the more expansive metal on the outside, while thecompensating bimetallic strip 142 is wound with the more expansive metalon the inside.

The initial current through the resistor 70 heats the main bimetallicstrip 124 and causes it to become wound more tightly so that the contact66 engages the contact 68. The compensating bimetallic strip 142 isremote from the resistor 70 and thus is heated very little by theresistor. After the contacts 66 and 68 are closed, the resistor 70 is nolonger heated, but the bimetallic strip 124 is heated by the loadcurrent. Very little of the load current passes along the compensatinglbimetallic strip 142, because most of the load current is carried bythe flexible lead 146. When the load current is interrupted, the mainbimetallic strip 124 cools off and is effective to open the contacts 66and 68. The resistor 70 is of such a high value that it eliminates theshock hazard at the broken glass heating element.

It will be recognized that the present invention provides efiectivemeans for obviating the shock hazard when electrically heated glass isbroken. The control devices of the present invention are eifective todisconnect the electrical power from the glass, or to diminish thesupply of power to such an extent that the shock hazard is eliminated.While the anti-shock control devices of the present invention areeffective in operation, they are extremely low in cost and easy tomanufacture.

Various other modifications, alternative constructions, and equivalentsmay be employed without departing from the true spirit and scope of theinvention, as exemplified in the foregoing description and defined inthe following claims.

We claim:

1. Fully automatic electrical heating apparatus,

comprising the combination of a plural pane glass pane1 having aninaccessible surface with a heating element mounted thereon,

a power line for receiving electric power,

switching means connected between said power line and said heatingelement,

first electrically operable automatic means for efiectively closing saidswitching means in response to the application of power to said powerline,

the closure of said switching means being effective to supply normalload current to said heating element from said power line,

and second means responsive to the interruption of the normal loadcurrent to cause the opening of said switching means,

so as to obviate any shock hazard in the event of breakage of said glasspanel.

2. Apparatus according to claim 1,

in which said switching means comprise a pair of normally open relaycontacts,

said first means comprising a voltage responsive element connectedbetween said power line and said heating element for causing closure ofsaid contacts,

said second means comprising a current responsive element connected tocarry the normal load current to said heating element for maintainingthe closure of said contacts,

whereby said contacts will open in response to interruption of thenormal load current,

said voltage responsive element having a high impedance in relation tothe applied voltage such that the current through said voltageresponsive element when said switching means are open is limited to avalue which does not present a shock hazard to human health.

3. Apparatus according to claim 1,

in which said switching means comprise a pair of contacts connectedbetween said power line and said heating element,

and a bimetal for carrying one of said contacts,

said first means comprising a first heater adjacent said bimetal andeffectively connected across said contacts for causing said bimetal toclose said contacts,

said second means comprising a second heater connected to carry saidnormal load current for heating said bimetal to maintain closure of saidcontacts,

whereby the breakage of said heating element is effective to de-energizesaid second heater while preventing energization of said first heater,

said first heater having a high resistance in relation to the appliedvoltage such that the current through said first heater is limited to avalue which does not present a shock hazard to human health.

4. Apparatus according to claim 1,

in which said switching means comprise a pair of normally open contactsconnected between said power line and said heating element,

and a bimetal for carrying one of said contacts,

said first means comprising a first resistance adjacent said bimetal andeifectively connected across said contacts for heating said bimetal tocause closure of said contacts,

said second means comprising a second resistance for carrying the normalload current to heat said bimetal and maintain the closure of saidcontacts,

the breakage of said heating element being etfective to de-energize saidsecond resistance while preventing energization of said firstresistance,

said first resistance having a high value in relation to the appliedvoltage such that the current through said first resistance is limitedto a value which does not present a shock hazard to human health.

5. Apparatus according to claim 4,

in which said second resistance comprises the selfcontained resistanceof said bimetal.

6. Apparatus according to claim 1,

in which said switching means comprise a pair of normally open contactsconnected between said power line and said heating element for supplyingthe normal load current to said heating element,

and a bimetal for carrying one of said contacts,

said first means comprising a resistance heater adjacent said bimetaland eifectively connected across said contacts for causing said bimetalto close said concontacts,

said second means comprising means for causing said load current to fiowalong said bimetal whereby said bimetal is heated by said load currentto maintain the closure of said contacts,

the breakage of said glass panel being efiective to interrupt the loadcurrent along said bimetal while preventing the energization of saidresistance heater,

/ said resistance heater having a high resistance in relation to theapplied voltage such that the current through said resistance heater islimited to a value which does not present a shock hazard to humanhealth.

7. Apparatus according to claim 6,

in which said bimetal is in the form of a generally helical member,

said resistance heater being'mounted within said helical member.

8. Apparatus according to claim 6,

in which said bimetal is in the form of a helical member, I

said resistance heater being disposed within said helical member,

said resistance heater having a first end lead supporting one end ofsaid helical member,

one of said contacts being supported by the other end of said helicalmember,

said resistance heater having a second end lead supporting the othercontact.

9. Apparatus according to claim 1,

in which said switching means comprises a pair of normally open contactseffectively connected between said power line and said heating element,

said first means comprising a relatively high impedance coil eflectivelyconnected across said contacts for closing said contacts,

said second means comprising a relatively low impedance coil effectivelyconnected in series with said contacts for maintaining the closure ofsaid contacts,

whereby the interruption of the normal load current through said-lowimpedancecoil will cause the opening of said contacts, i

said high impedance coil being effective to obviate any shock hazard atsaid heating element.

10. Apparatus according to. claim 1,

in which said switching means comprises a' series of three contacts,

a contactor movable successively to said contacts,

and a bimetal carrying said contactor,

said first means comprising a first resistance heater adjacent saidbimetal and having an energizing circuit connected to the first of saidcontacts for initially heating said bimetal and causing said bimetal tomove said contactor to the second and third of said contacts,

said second means comprising means for causing the normal load currentto flow through said bimetal and said contactor to said third contactfor heating said bimetal and thereby maintaining said contactor againstsaid third contact,

and a holding resistance having an energizing circuit connected to saidsecond contact for heating said bimetal to hold said contactor againstsaid second contact upon the return of said contactor when the normalload current is interrupted.

11. Apparatus according to claim 10,

in which said holding resistance is connected from said second contactto said first contact and thus to said first resistance heater.

12. Apparatus according to claim 1,

in which said switching means comprises first, second and thirdcontacts,

a contactor initially engaging said first contact and movable to saidsecond and third contacts,

and a bimetal for moving said contactor,

said first means compressing a first resistance heater adjacent saidbimetal and having an energizing circuit connected to said first contactfor initially heating said bimetal to move said contactor to said secondand third contact,

said contactor and said third contact being effective to carry thenormal load current,

said second means comprising means for causing the normal load currentto heat said bimetal for maintaining said contactor against said thirdcontact while causing said contactor to return to said second contactupon interruption of the load current,

and a second resistance having an energizing circuit connected to saidsecond contact for heating the bimetal to maintain the contactor againstsaid second contact.

13. Apparatus according to claim 12,

in which said second resistance is connected from said second contact tosaid first contact and thus to said first resistance heater.

14. Apparatus according to claim 12,

in which said means comprises circuit connections for causing the normalload current to flow along said bimetal to heat said bimetal.

15. Electrical heating apparatus,

comprising the combination of a glass panel having an inaccessiblesurface with a heating element mounted thereon,

a power line for receiving electric power,

switching means connected between said power line and said heatingelement,

first electrically operable means for effectively closing said switchingmeans in response to the application of power to said power line,

the closure of said switching means being elfective to supply normalload current to said heating element from said power line,

second means responsive to the interruption of the normal load currentto cause the opening of said switching means, so as to obviate any shockhazard in the event of breakage of said glass panel,

said switching means comprising a pair of contacts connected betweensaid power line and said heating element for carrying the normal loadcurrent,

a bimetal for carrying one of said contacts,

' said first means comprising a' resistance heater effectively connectedacross said contacts for heating said bimetal to close said contacts,

said second means comprising means for causing said normal load currentto heat said bimetal to maintain the closure of said contacts,

and a compensating bimetal for carrying the other contact to compensatefor the etfects of ambient temperature variations on said firstmentioned bimetal,

said resistance heater having a high resistance in relation to theapplied voltage such that the current through said resistance heater islimited to a value which does not present a shock hazard to humanhealth.

16. An anti-shock control device for electrically heated glass or thelike,

comprising the combination of a pair of normally open contacts to carrythe normal load current,

a bimetal carrying one of said contacts,

a resistance heater effectively connected across said contacts forheating said bimetal and thereby causing the closure of said contacts,

means for causing the normal heating current through said contacts toheat said bimetal and thereby maintain the closure of said contacts,

whereby the interruption of the normal load current causes the openingof said contacts,

said resistance heater having a high value in relation to the appliedvoltage such that the current through said resistance heater when saidcontacts are open is limited to a value which does not present a shockhazard to human health,

and a compensating bimetal for carrying the other contact to compensatefor the efiects of ambient temperature variations on saidfirst-mentioned bimetal.

17. A control device according to claim 16,

said means comprising circuit connections for causing the normal loadcurrent to flow along said firstmentioned bimetal while avoiding theflow of the load current along said compensating bimetal.

18. A control device according to claim 7,

in which said first mentioned bimetal is in the form of a first helicalmember,

said resistance heater being disposed within said first helical member,

said resistance heater having a first end lead supporting one end ofsaid first helical member,

said one contact being mounted on the other end of said first helicalmember,

said compensating bimetal being in the form of a second helical memberhaving one end supporting the other contact,

said resistance heater having a second end lead extending within saidsecond helical member and supporting the other end thereof,

said compensating bimetal being effective to compensate for the effectsof ambient temperature variations on said first-mentioned bimetal.

19. Fully automatic electrical heating apparatus,

comprising the combination of a plural pane glass panel having aninaccessible surface with a heating element mounted thereon,

a power line for receiving electric power,

normally open switching means connected between said power line and saidheating element,

first electrically operable automatic means responsive to thedevelopment of substantial voltage across said switching mean forclosing said switching means to cause said switching means to carry thenormal load current to said heating element,

and second means for causing the normal load current to maintain theclosure of said switching means while causing the opening of saidswitching means in response to the interruption of said load current,

said switching means being arranged to inactivate said firstelectrically operable means in response to closure of said switchingmeans.

20. A control device according to claim 19,

in which said switching means comprises a pair of contacts and a bimetalfor closing said contacts,

said first means comprising a first resistance heater for heating saidbimetal to close said contacts,

said second means comprising a heating circuit for causing the loadcurrent through said contacts to heat said bimetal,

said first resistance heater having a high value in relation to theapplied voltage such that the current through said first resistanceheater is limited to a value which does not present a shock hazard tohuman health.

21. A control device according to claim 19,

in which said switching means comprises a pair of normally open relaycontacts,

said first means comprising a high impedance coil elfectively connectedacross said contacts for closing said contacts,

and a low impedance coil elfectively connected in series with saidcontacts for maintaining the closure thereof,

said high impedance coil having an impedance which is high in relationto the applied voltage such that the current through said high impedancecoil is limited to a value which does not present a shock hazard tohuman health.

References Cited UNITED STATES PATENTS 2,403,803 7/1946 Kearsley 219-511X 2,417,778 3/ 1947 Osterheld 219-512 X 2,448,289 8/1948 Anderson219-511 2,499,906 3/1950 Crise 219-511 2,756,382 7/ 1956 Wuerth 323-682,806,118 9/1957 Peterson 21 9-203 2,914,637 11/1959 Wuerth 200-1222,945,933 7/1960 Girolano et al. 200-122 3,330,942 7 1967 Whitson219-522 2,557,905 6/1951 Burton et a1. 219-522 X 2,898,433 8/1959 Felt219-202 X 3,379,859 4/1967 Marriott 219-522 3,449,551 6/ 1969 Aisanich219-522 X VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R.

Patent No. ,753 Dated Sept. 1, 1970 Inventor(s) D. J. Aisanich et al Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 4, line 43, change "resistors" to "resistor."

Column 11, line 9, change "7" to "16." Column 11, line 36, change "mean"to "means."

SiGNED AND QEALED 6EAL) Amen:

EdwardMFIctchcr, Ir. mm E. SGHUYIER, m-

L office? emissions:- of Patents J

